As neuroscience provides new advances into understanding human brain function, an improved assessment technology is required to characterize the functional neurophysiology of sleep. The fMRI and PET methods of cerebral blood flow imaging face limitations in characterizing sleep organization because their measurement technologies (such as head fixation and loud scanning noise) are problematic for normal sleep. Furthermore, sleep neurophysiology involves many rapid events that must be described with millisecond temporal resolution. We propose to develop the SOMNA (Sleep Organization and Microstates of Neural Arousal) assessment system for dense sensor array electroencephalographic (EEG) studies of sleep. The improved spatial sampling of the 128- and 256- channel EEG will correct an important inadequacy of conventional EEG, promising more accurate anatomical analysis of sleep neurophysiology. The SOMNA system would provide advanced computerized assessment of sleep EEG and polysomnographic measures, and it would segment the EEG into microstates of arousal as well as traditional sleep stages. The system would advance the technology of clinical sleep laboratories, providing new methods of dense array EEG for studies of current density, electrical field animations, and MR-constrained source localization. The improved understanding of sleep physiology may be important to clinical sleep disorders including insomnia, epilepsy, and sleep apnea. PROPOSED COMMERCIAL APPLICATIONS: The ease of testing and interpretation with the SOMNA system will be attractive not only to sleep research centers, but to clinical sleep laboratories, integrating the Digital EEG and Sleep Polysomnography functions in many hospitals and neurology clinics.